This invention relates to alignment of liquid crystals (LCs), and more particularly to liquid crystal photoalignment.
LCs include liquids in which an ordered arrangement of molecules exists. Typically, LC molecules are anisotropic, having either an elongated (rod-like) or flat (disk-like) shape. As a consequence of the ordering of the anisotropic molecules, a bulk LC often exhibits anisotropy in its physical properties, such as anisotropy in its mechanical, electrical, magnetic, and/or optical properties.
As a result of the rodlike or disklike nature, the distribution of the orientation of LC molecules typically plays an important role in optical applications, such as in liquid crystal displays (LCDs). In these applications, LC alignment is dictated by an alignment surface. The alignment surface is usually treated so that the LC aligns relative to the surface in a predictable and controllable way. In many cases, the role of the alignment surface is to ensure a single domain through the LC device. In the absence of a treated alignment surface, the LC will typically have many domains and many disclinations, or discontinuities in orientation. In optical applications, these domains and discontinuities can cause scattering of light, leading to a degradation in the performance of the display.
In many LCDs, the alignment surfaces provide homogeneous alignment of the LC at the surface. Such an alignment surface may be provided by rubbing a polymer, such as a polyimide, in a direction parallel to the desired alignment direction. Rubbing may be performed using a cloth, such as a felt or velvet fabric. It is generally believed that rubbing a polymer surface produces a uniform and unidirectional tilt of dangling bonds or polymer chains on the surface. The unidirectional tilt of these surface molecules may lead to the parallel homogeneous alignment of the LC molecules.